Splitting files into subdirectories in preparation for merge

lib/cache_toolbox/model.py

@@ -0,0 +1,78 @@
+"""
+Caching model instances
+-----------------------
+
+``cache_model`` adds utility methods to a model to obtain ``ForeignKey``
+instances via the cache.
+
+Usage
+~~~~~
+
+::
+
+    from django.db import models
+    from django.contrib.auth.models import User
+
+    class Foo(models.Model):
+        name = models.CharField(length=20)
+
+    cache_model(Foo)
+
+::
+
+    >>> a = Foo.objects.create(name='a')
+    >>> a
+    <Foo: >
+    >>> Foo.get_cached(a.pk) # Cache miss
+    <Foo: >
+    >>> a = Foo.get_cached(a.pk) # Cache hit
+    >>> a.name
+    u'a'
+
+Instances returned from ``get_cached`` are real model instances::
+
+    >>> a = Foo.get_cached(a.pk) # Cache hit
+    >>> type(a)
+    <class '__main__.models.A'>
+    >>> a.pk
+    1L
+
+Invalidation
+~~~~~~~~~~~~
+
+Invalidation is performed automatically upon saving or deleting a ``Foo``
+instance::
+
+    >>> a = Foo.objects.create(name='a')
+    >>> a.name = 'b'
+    >>> a.save()
+    >>> a = Foo.get_cached(a.pk)
+    >>> a.name
+    u'b'
+    >>> a.delete()
+    >>> a = Foo.get_cached(a.pk)
+    ... Foo.DoesNotExist
+"""
+
+from django.db.models.signals import post_save, post_delete
+
+from .core import get_instance, delete_instance
+
+def cache_model(model, timeout=None):
+    if hasattr(model, 'get_cached'):
+        # Already patched
+        return
+
+    def clear_cache(sender, instance, *args, **kwargs):
+        delete_instance(sender, instance)
+
+    post_save.connect(clear_cache, sender=model, weak=False)
+    post_delete.connect(clear_cache, sender=model, weak=False)
+
+    @classmethod
+    def get(cls, pk, using=None):
+        if pk is None:
+            return None
+        return get_instance(cls, pk, timeout, using)
+
+    model.get_cached = get